Brown stain suppressing phenol free and chlorinated hydrocarbons free photoresist stripper

ABSTRACT

Stripping solution compositions which avoid the problem know as &#34;brown staining&#34; are provided. Relevant stripping solutions are those that are free from phenol and chlorinated hydrocarbon compounds and comprise a surfactant alkylarylsulfonic acid having 12-20 carbons, a hydrotropic aromatic sulfonic acid having 6-9 carbons and a halogen-free aromatic hydrocarbon solvent with a boiling point above 150° C. To suppress brown staining, a water soluble sulfone is incorporated into the stripping solution. The stripping compositions effectively remove organic polymeric substances from inorganic substrates and are substantially clear water rinsable.

BACKGROUND OF THE INVENTION

This invention relates to stripping solutions for removing polymericorganic materials coated onto various metal, metal oxide, glass orinsoluble polymeric substrate surfaces and provides organic mixturescomprised of sulfonic acids, hydrocarbons and sulfones, constituted insuch a way to be compatible with aluminum and semiconductor manufacture.Specifically, this invention provides a sulfonic acid-hydrocarbon basedstripping solution that will not generate brown stains on aluminumsubstrate during semiconductor processing of substrate aluminum.

During manufacture of semiconductors and semiconductor microcircuits, itis frequently necessary to coat the materials from which thesemiconductors and microcircuits are manufactured with a polymericorganic substance, generally referred to as a photoresist, e.g., asubstance which forms an etch resist upon exposure to light. Thesephotoresists are used to protect selected areas of the surface of thesustrate, e.g., silicon, SiO₂ or aluminum, from the action of theetchant while such etchant selectively attacks the unprotected area ofthe substrate. Following completion of the etching operation and washingaway of the residual etchant, it is necessary that the resist be removedfrom the protective surface to permit essential finishing operations.

A common method used in removing the photoresist from the substrate isby contacting the substrate with an organic stripper. These organicstrippers in the past have been composed of various components whosepurpose it was to lift and remove the polymeric photoresist from thesubstrate and usually contained phenol or phenol compounds andchlorinated hydrocarbon compounds. The use of phenol or phenol compoundsor chlorinated hydrocarbon compounds results in a distinct disadvantagedue to the toxicity of phenol as well as the pollution problems arisingfrom the disposal of phenol or phenol compounds such as cresols, phenolsulfonic acid and the like or the disposal of chlorinated hydrocarboncompounds. U.S. Pat. No. 4,165,294 discloses stripping solutions thatare phenol-free and chlorinated hydrocarbon-free and that are waterrinsable.

The stripping solutions of U.S. Pat. No. 4,165,294 while performingeffectively have been found to have the drawbacks of generating brownstains during processing, particularly on aluminum substrates, used insemiconductor elements. Brown stains of this character are unsightly andin some cases affect performance. Both of these drawbacks areundesireable. It is accordingly indicated that a need exists for aphenol-free and chlorinated hydrocarbon-free stripping solution which inuse do not evidence a brown stain of the semiconductor substrate.

SUMMARY OF THE INVENTION

The present invention provides an improvement in stripping compositionsof the kind disclosed in U.S. Pat. No. 4,165,294 in that it obviates aproblem involving adverse effects on substrate metals, principallyaluminum, which is known to occur with stripping compositions of thekind disclosed in that patent. This problem commonly takes the form of abrown stain visible on aluminum bonding a contact pads under 50 to 100Xmagnification. Since brown bond pad formation is undesired insemiconductor processing, use of sulfonic acid based strippers isjeopardized.

The invention has an object to provide a stripping solution that willnot interact adversely with substrates, particularly aluminum, to form astaining effect which is undesireable in semiconductor manufacture. Itis a further object of the invention to provide an improved strippingsolution that affords enhanced processing characteristics. These andother objects of the invention will become apparent from the descriptionof the invention which follows.

The formulations employed in the present invention are composed toprovide a stripping solution free of phenolics and chlorinatedhydrocarbons such that the mixture of sulfonic acids functions in such away that photoresists are clearly dissolved from substrate surfaces andoil-free water rinsing results.

In accordance with the invention, sulfones, preferably those that arewater soluble, are incorporated into the stripping compositions andleave the effect of suppressing the tendency to stain the semiconductorsubstrate, a drawback which is especially prevalent on aluminum bondpads. To avoid particle generation during water rinsing which may resultfrom use of sulfones that are not water soluble, sulfones that aresubstantially soluble in water are preferred. The sulfones contemplatedfor use in accordance with the present invention are those of theformula

    R.sup.1 SO.sub.2 R.sup.2

wherein R¹ and R² may be the same or different and are radicals selectedfrom the group consisting of alkyl and aryl radicals having the valuestabulated as follows:

    ______________________________________                                          R.sup.1            R.sup.2                                                  ______________________________________                                        CH.sub.3, C.sub.2 H.sub.5,                                                                       CH.sub.3, C.sub.2 H.sub.5,                                 C.sub.3 H.sub.7, C.sub.6 H.sub.5 CH.sub.2                                                        C.sub.3 H.sub.7, C.sub.6 H.sub.5 CH.sub.2                  Xη(C.sub.6 H.sub.5 --η)--                                                                Xη(C.sub.6 H.sub.4 --η)--SO.sub.3 H                X = H, CH.sub.3, C.sub.2 H.sub.5                                                                 X = H, CH.sub.3, C.sub.2 H.sub.5                           η = 1-5        η = 1-4                                                Xη(C.sub.6 H.sub.4 --η)SO.sub.3 H                                                        Xη(C.sub.6 H.sub.4 --η)SO.sub.3 H                  X = H, CH.sub.3, C.sub.2 H.sub.5                                                                 X = H, CH.sub.3, C.sub.2 H.sub.5                           CH.sub.3 (CH.sub.2)ηC.sub.6 H.sub.5 --                                                       CH.sub.3 (CH.sub.2)ηC.sub.6 H.sub.5 --                 η = 8-12       η = 8-12                                               ______________________________________                                    

and

Cyclic structures wherein R¹ is linked to R² and have the formula

    (CH.sub.2).sub.ηSO.sbsb.2

    η=4-7

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a composition which is effective inremoving photoresist, both positive and negative type, and a method forremoving photoresist from inorganic substrates, without the use ofphenol or phenol compounds or chlorinated hydrocarbon compounds andtheir corresponding disadvantages. The surfactant sulfonic acid actseffectively as a photoresist stripper.

The surfactant sulfonic acids that have been found to be effective forremoving organic photoresist are those having 12-20 carbons.

Exemplary of such aryl sulfonic acids suitable for use in accordancewith the present invention are hexylbenzene sulfonic acid,heptylbenzenesulfonic acid, cotylbenzenesulfonic acid,decylbenzenesulfonic acid, dodecylbenzenesulfonic acid,tridecylbenzenesulfonic acid, quadecylbenzenesulfonic acid, and thelike.

Blends of these surfactant sulfonic acids may also be employed so longas the number average carbon number is between 12 and 20. Solutionscontaining a major proportion of higher sulfonic acid of over 15carbons, which is particularly dodecylbenzenesulfonic acid are among thepreferred blends.

The preferred surfactant sulfonic acid for use in accordance with thisinvention is dodecylbenzenesulfonic acid although decylbenzenesulfonicacid may also be used.

The solvent or solvent system which are to be used must be materialswhich do not deter from the stripping effectiveness of the surfactantsulfonic acid. The solvent or solvent system itself is not critical tothe stripping, i.e., the function of the sulfonic acid, since thefunction of the solvent is merely to reduce the viscosity and to renderthe sulfonic acid more readily water rinsable. Of course, the solventshould be miscible with the sulfonic acid and not react therewith andthe most desirable solvents are those which do not induce corrosion onmaterials such as aluminum. For the present invention, the solvent mustnot contain chlorinated hydrocarbons, phenol or phenol compounds.

Preferred components of the aromatic hydrocarbon solvent are alkylarylcompounds having 1-14 alkyl carbons. Such compounds contain a benzenering with one or more alkyl chains. Each alkyl chain may be straight orbranched, but the straight-chain alkyl groups are preferred forbiodegradability. Preferred examples of such compounds include toluene,xylene, ethylbenzene, trimethylbenzene, cumene, phenyloctane,dodecylbenzene, phenyl nonane, tridecylbenzene, tridecyltoluene andtriethylbenzene and mixtures of such compounds. The preferred aromatichydrocarbon solvents are mixtures of compounds with 9-13 alkyl carbonsor 15-19 total carbons, dodecylbenzene, or mixtures having an average ofabout 18 total carbons.

The composition is free of halogenated hydrocarbons such asperchloroethylene and dichlorobenzene. Such solutions are generallybiodegradable as compared to solutions containing halogenatedhydrocarbons.

Other solvents may also be used provided they are free of phenol, phenolcompounds and chlorinated hydrocarbon free. However, such othercomponents are preferred only in smaller quantities than the aromatichydrocarbon.

The present invention also includes a hydrotropic aromatic sulfonic acidof 6-9 carbons which may be benzenesulfonic acid, toluenesulfonic acid,xylenesulfonic acid, ethylbenzenesulfonic acid,methylethylbenzenesulfonic acid, trimethylbenzenesulfonic acid,propylbenzenesulfonic acid, cumenesulfonic acid or mixtures thereof. Thetotal group of names hydrotropic sulfonic acids will sometimes bereferred to herein as "hydrotropes" and the group excluding benzenesulfonic acid will be referred to as "alkylaryl hydrotropes." It shouldbe appreciated that the alkylaryl hydrotropes have 7-9 carbons.Preferred are toluenesulfonic acid and benzenesulfonic acid, withbenzenesulfonic acid being more preferred. The severalalkylbenzenesulfonic acids may be one isomer such as paratoluene acid ora mixture of isomers such as para and orthotoluenesulfonic acid.

It has been found that although the stripping compositions disclosed inthe above noted U.S. Pat. No. 4,165,294 are stabilized against metalcorrosion such as by a fluoride inhibitor and are substantiallyanhydrous, i.e., contain less than 1% water, again to prevent metalcorrosion, nevertheless the aforementioned undesirable brown staining ofsubstrate still occurs. This "staining" effect, caused by a deposit ofundetermined composition originating in the stripper is particularlynoticed following photoresist removal of the opening bonding pads. Inaccordance with the discovery of the present invention, this stainingeffect is avoided by including a minor amount, i.e., about 0.5 to about10 weight percent and preferably about 1 to about 5 weight percent, of awater soluble sulfone type material in the stripper. Water solubility isimportant to avoid precipitation of solids during the water rinsingstage following stripping. Preferably dialkyl (i.e., (dimethyl,diethyl), cyclo-alkyl (i.e., sulfolane) and sulfonated diarylsulfones(i.e., mono and disulfonic acids from diphenol sulfone, ditolyl anddixylylsulfone).

In accordance with the invention the problem involving the adverseeffects resulting from the stripping solution disclosed in U.S. Pat. No.4,165,294 on the substrate metals on which such stripping compositionsare used in the course of semiconductor manufacture, and referred toherein as "brown staining", may be avoided by the use of a sulfolaneadditive in the composition. The brown staining, which is particularlyvisible on aluminum bonding contact pads under 50 to 100X magnification.This staining effect is so objectionable in semiconductor processingthat unless the brown stain effect can be avoided, the use of suchsulfonic acid strippers would be discontinued by commercial processors.

This invention incorporates water soluble sulfones into sulfonicacid-hydrocarbon stripping solutions in order to suppress staining ofaluminum bond pads with water solubility preferred in order to avoidparticle generation during water rinsing steps stemming from processingof water insoluble sulfones.

The following formulation provides a stripping solution free ofphenolics and chlorinated hydrocarbons, and may be used with varioussulfonic acids that functions in such a way that photoresists areclearly dissolved from substrate surfaces and with oil free waterrinsing results. This formulation has the following compositions:

    ______________________________________                                                          Weight Parts                                                ______________________________________                                        Benzene Sulfonic Acid                                                                             35.5                                                      Xylene Sulfonic Acid                                                                              15.2                                                      Dodecylbenzene Sulfonic Acid                                                                      45.8                                                      Dodecylbenzene      1                                                         Sulfolane           2.0                                                       HF (as malononitrile complex)                                                                     200 ppm                                                   H.sub.2 O           0.3%                                                      H.sub.2 SO.sub.4    .3                                                        ______________________________________                                    

The sulfones as a class have the general formula R¹ SO₂ which may beemployed in accordance with the invention and can be either aryl oralkyl.

The values for R¹ and R² for the sulfones incorporated in thephotoresist stripping compositions are summarized as follows:

    ______________________________________                                          R.sup.1            R.sup.2                                                  ______________________________________                                        CH.sub.3, C.sub.2 H.sub.5,                                                                       CH.sub.3, C.sub.2 H.sub.5,                                 C.sub.3 H.sub.7, C.sub.6 H.sub.5 CH.sub.2                                                        C.sub.3 H.sub.7, C.sub.6 H.sub.5 CH.sub.2                  Xη(C.sub.6 H.sub.5 --η)--                                                                Xη(C.sub.6 H.sub.4 --η)--SO.sub.3 H                X = H, CH.sub.3, C.sub.2 H.sub.5                                                                 X = H, CH.sub.3, C.sub.2 H.sub.5                           η = 1-5        η = 1-4                                                Xη(C.sub.6 H.sub.4 --η)--SO.sub.3 H                                                      Xη(C.sub.6 H.sub.4 --η)SO.sub.3 H                  X = H, CH.sub.3, C.sub.2 H.sub.5                                                                 X = H, CH.sub.3, C.sub.2 H.sub.5                           CH.sub.3 (CH.sub.2) ηC.sub.6 H.sub.5 --                                                      CH.sub.3 (CH.sub.2)ηC.sub.6 H.sub.5 --                 η = 8-12       η = 8-12                                               ______________________________________                                    

Cyclic structures wherein R¹ is linked to R² and have the formula

    (CH.sub.2)ηSO.sub.2

    η=4-7

In use, sulfonic acid-hydrocarbon mixtures as included in (Table I ofU.S. Pat. No. 4,165,294) will generate a thin layer of material(deposit) on aluminum surfaces exposed to the stripping solution duringsemiconductor processing. This deposition, which appears brown under50-100X magnification, does not form continuously but rather as afunction of stripper composition, stripping bath life and stripping bathtemperature. Once the staining cycle is known for a given mixture theabsence of staining can be achieved by including low concentration ofsulfones to the stripping formulation.

EXAMPLE 1

A sulfonic acid mixture suitable for removing photoresist from aluminumcontaining semiconductor substrates without causing browning wasprepared as follows: 50 wt. parts of benzene sulfonic acid (a mixture ofhydrotropic sulfonic acids e.g., benzenesulfonic acid, toluenesulfonicacid, xylenesulfonic acid, ethylbenzene sulfonic acids may also beused), 48 wt. parts dodecylbenzene sulfonic acid containing 6%dodecylbenzene and 2 wt. parts sulfolane were mixed and 2800 ppm of acomplex formed from malono-nitrile and hydrofluoric acid (2:1 mol ratiomalono-nitrile to HF) is dissolved in the resulting stripping solutionto prevent corrosion of aluminum metal during photoresist stripping fromsemiconductor substrates. In use, this stripping solution iscomparatively free of brown staining.

EXAMPLE 2

A second stripping solution suitable for use in processing aluminumsemiconductors is prepared utilizing the components in proportionsdescribed in Example 1. Diphenylsulfone monosulfonic acid is substitutedfor sulfolane. This solution when compared with a solution in which thediphenylsulfone monosulfonic acid is omitted is relatively free of brownstaining.

EXAMPLE 3

A third stripping solution suitable for use in processing aluminumsemiconductors is prepared utilizing the components in proportionsdescribed in Example 1. Diphenylsulfone disulfonic acid is substitutedfor sulfolane with results comparable to those obtained with thestripping solution of Example 2.

I claim:
 1. A composition for stripping photoresist from an inorganicsubstrate comprising in combination:(a) from about 5 to about 60 weightpercent of an alkarylsulfonic acid surfactant having 12-20 carbon atoms;(b) from about 5 to about 95 weight percent of a hydrotropic sulfonicacid having 6-9 carbons; (c) from 0 to about 40 weight percent of ahalogen-free aromatic hydrocarbon solvent with a boiling point above150° C.;and (d) from about 0.5 to about 10 weight percent of asubstantially water soluble sulfone of the formula

    R.sup.1 SO.sub.2 R.sup.2

where R¹ and R² may be the same or different and are selected from thegroup consisting of alkyl radicals, aryl radicals and alkylaryl radicalsof 1 to 20 carbon atoms and including cyclic structures wherein R¹ islinked to R² and have the formula

    (CH.sub.2).sub.n SO.sub.2

wherein is 4 to 7; said composition being free of phenol compounds andchlorinated hydrocarbon compounds and being substantially clear waterrinsable.
 2. The composition of claim 1 wherein (d) is sulfolane.
 3. Thecomposition of claim 1 wherein (a) is dodecylbenzenesulfonic acid. 4.The composition of claim 1 wherein (c) is dodecylbenzene.
 5. Thecomposition of claim 3 wherein (d) is sulfolane.
 6. The composition ofclaim 5 wherein (c) is dodecylbenzene.
 7. The composition of claim 1wherein (d) is present in amounts of from about 1 to about 5 weightpercent.